Mobile radio handsets often incorporate multiple radios that operate over different protocols and different frequency bands, each of which must operate with an antenna tuned to the relevant band. Typically, near-field communications (NFC, a member of the broader radio frequency identification RFID technologies), Bluetooth, wireless local area network WLAN, and global positioning systems GPS are implemented with separate antennas. Where the handset also includes an internal frequency modulated FM radio, typically there is also an internal FM receiver (RX) including antenna and an internal FM transmitter (TX) with an antenna that may be separate from the FM-RX antenna.
All of this hardware of course must be fit into a handheld-size package, of which the housing itself and the user's hand placement thereon must either facilitate the proper antenna resonances or at least not interfere. This problem of space is generally more acute if the handset housing is metal as with the Nokia N8 handset rather than plastic as has been recently common. The overall electronics layout in the handset must account for antennas to support cellular radio(s) as well as secondary radios such as Bluetooth, WLAN, GPS, RFID/NFC, and/or FM as the case may be. While some of those secondary radio antennas can be made quite small, typically the FM antenna(s) and the RFID/NFC antenna require much more space than the others.
Utilizing one physical antenna radiator for multiple different-band radios simplifies the electronics layout and eases the physical space constraints. By example a Bluetooth/WLAN antenna combined to a FM band radiator is known, often utilizing an unbalanced (non-loop) configuration for the FM TX antenna. But there is an additional challenge in such a combined antenna in that it is difficult to get sufficient output power to the physically large FM-TX antenna radiator element. Satisfying the dual constraints of space and output power are particularly challenging for a small package such as a mobile handset.
Typically, FM-TX antennas for hand-portable devices are implemented as a coil or monopole type antenna. NFC antennas are typically implemented as a coil or winding of conductive material which is fed differentially (balanced). As above, both are relatively large in the context of mobile handsets. In the above referenced co-owned U.S. patent applications there is an embodiment in which both RFID/NFC and FM-TX radios are connected to the same antenna feed using filters for proper frequency isolation of the different bands.
Certain prior art approaches for coil antennas for NFC and/or FM-TX uses may be seen by example at EP Patent Publications 1,966,852, 2,065,969, 2,219,265 and 2,221,914; and further at US Patent Publications 2008/0081631 and 2008/0233868.